1. Field of the Invention
The present invention relates to an image data reproducing method and an image data reproducing apparatus for reading compressed image data from a recording medium so as to reproduce the image data, and relates to an image data recording method and an image data recording apparatus for compressing image data so as to write the compressed image data onto a recording medium.
2. Description of the Related Art
In recent years, DVD as an information recording medium which is capable of recording an extremely great capacity of data with high density has spread. Image data are recorded onto such a DVD by using a digital image compressing technique such as MPEG2 (Moving Picture Expert Group 2) so that an image with excellent image quality can be reproduced and a film can be reproduced for a long time.
A DVD video format is suggested as the standard for recording image data onto DVD. The DVD video format has a lot of functions in order to apply DVD widely to various uses. One example of the functions is a multi-angle function. An image imaged from a plurality of angles can be reproduced by using the multi-angle function while changing the angles. For example, an angle on a predetermined scene of a film or the like is selected by a user according to the user's preference, and the predetermined scene can be reproduced from the selected angle for a definite time.
In order to realize the multi-angle function, at the time when an angle is changed, it is necessary to change an on-reproducing image seamlessly without a break.
In order to realize the seamless reproduction, a recording method which is called interleaved recording is used for recording image data onto DVD. The interleaved recording is a technique to divide recording data into a plurality of interleaved units per each of the plural angles and record them alternatively onto the DVD. When one angle is selected from the plural angles and reproduction is executed, only an interleaved unit corresponding to the selected angle is extracted from the DVD, and the interleaved units are stored one after another onto a buffer memory. Then, the stored interleaved units are read one after another from the buffer memory so as to be reproduced. Since a speed of reading from DVD is faster than a speed of reproducing image data, as long as a capacity of the buffer memory is secured appropriately, the image data can be reproduced seamlessly. Further, an upper limit of a size in the interleaved units is limited in order to shorten a jump distance on DVD in an pick-up. This is because when the jump distance on the DVD in the pick-up is longer, a period for stopping data reading becomes longer, and thus continuity of image reproduction is lost.
Incidentally, according to the above-mentioned general multi-angle function, one angle can be selected from a plurality of angles and reproduction can be executed. However, in the multi-angle function, it is not possible to make images from a plurality of angles synchronize with each other so that the images of these angles are simultaneously reproduced. The reason for this is as follows.
As mentioned above, since it is required to realize the seamless reproduction, the upper limit of the size in the interleaved units is limited. However, an amount of image data included in each interleaved unit is not uniform. This is because as a compressing method which is used for recording image data onto DVD, a variable rate compressing method where a compressing rate varies with image quality or the like is adopted. More specifically, as the compressing method which is used for recording image data onto DVD, a variable rate compressing method utilizing MPEG2 is adopted. Therefore, a data amount in each angle does not become uniform, and as a result an amount of image data included in each interleaved unit does not become uniform.
Furthermore, reading timing or writing timing of image data stored in a buffer memory generally changes depending on an amount of data stored in the buffer memory. When an amount of the image data included in each interleaved unit is not uniform, the reading timing or the writing timing cannot be determined periodically.
Since an amount of the image data included in each interleaved unit is not uniform, or the reading timing or the writing timing of the image data stored in the buffer memory is not uniform, it is difficult, in the general multi-angle function, that a plurality of angles are synchronized with each other and images from these angles are reproduced simultaneously.